Effect of erythromycin on myocardial repolarization in patients with community-acquired pneumonia

Background. Erythromycin has been associated with prolongation of myocardial repolarization and torsades de pointes (TdP). Methods. To determine the frequency, dose-response, and risk factors for erythromycin-associated prolongation of myocardial repolarization, we observed data of patients admitted to our hospital with pneumonia who were treated with erythromycin. Results. In 35 women and 28 men enrolled in this study, the QT, increased from 434 +/- 4 milliseconds at baseline to 464 +/- 5 milliseconds after receiving a cumulative dose of 3.2 +/- 0.2 g. of erythromycin. Neither age, sex, presence of preexistent congestive heart failure/coronary artery disease, electrolyte values, nor cumulative dose of erythromycin was associated with QT(c) prolongation. In 27 patients who received intravenous erythromycin for 3 days, the QT(c) increased from 427 +/- 5 milliseconds before to 461 +/- 8 milliseconds at 24 hours but did not increase further by day 3 (457 +/- 10 milliseconds). No patient in this cohort had TdP. Conclusions. Erythromycin therapy is associated with prolongation of myocardial repolarization that manifests after the first few doses in a majority of patients.